Someone realized putting a solid starter in the bullpen was a bad idea, and Carlos Zambrano is on his way back to the rotation. He'll pitch in long relief until he's stretched out enough to start. The Cubs are being coy, but it's pretty clear this is what's going on.
Other things that are clear:
1. Zambrano's four-seam fastball dominated his pitch mix while in relief, further exasperating (IMO) his decision to "drop" the cutter in 2010 (he hasn't altogether).
2. Zambrano's only effective pitch in relief was his fastball (rvERA is based on actual outcomes, rvERAe is based on outcomes derived from batted ball types -- in other words, it regresses batted ball outcomes to league average; reality is often somewhere in between). A case could be made for the splitter, too.
3. As shown above, he was more effective overall as a starter.
4. This one is about non-clarity -- was he throwing harder out of the bullpen?
Pitch SP RP
Sinker 91.2 91.2
Fastball 90.8 92.1
Slider 80.1 80.1
Splitter 84.3 83.5
Given the lack of secondary pitches, relatively speaking, in his relief appearances it may be easy to look at the fastball speed and go "yes, faster", but I'm not so sure.
I can dig up some more stuff (I have) but, given the small samples, I think I've done enough and still feel like I can say: Big Z couldn't use all his pitches as a reliever, and part of what makes him special is his extensive repertoire. He'll need time to get that feel back, not just the stamina, before he can go seven innings again.